APOD: Star Size Comparisons (2013 Jun 06)

[APOD Robot]

Star Size Comparisons

Explanation: How big is our Sun compared to other stars? In a dramatic and popular video featured on YouTube, the relative sizes of planets and stars are shown from smallest to largest. The above video starts with Earth's Moon and progresses through increasingly larger planets in our Solar System. Next, the Sun is shown along as compared to many of the brighter stars in our neighborhood of the Milky Way Galaxy. Finally, some of the largest stars known spin into view. Note that the true sizes of most stars outside of the Sun and Betelgeuse are not known by direct observation, but rather inferred by measurements of their perceived brightness, temperature, and distance. Although an inspiring learning tool that is mostly accurate, APOD readers are encouraged to complete the learning experience -- and possibly help make future versions more accurate -- by pointing out slight inaccuracies in the video.

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[Beyond]

We need a very much BIGGER word than HUMONGUS !!

[Deesqrd]

Planets and Sun are rotating in reverse.

[moonstruck]

Sh1t. And I don't usually talk like that ..but....

[Hugo]

It would be nice to have this video include black holes.

[geckzilla]

I have an interest in the way we visualize the larger stars. I know we've never resolved any star other than our sun into much more than a blurry blip 4 pixels across, so we may never have a direct image of one, but do we know enough about them to guess a little better at their appearance? For instance, would the edge of the star be so clearly defined or would it be kind of tattered like a cloud? Or maybe blurred like a fog settled close to the ground? Or perhaps there is a visible layering effect? I also wonder if we could look at the star a bit longer with our own eyes without some sort of filter.

[DRAKULIAN]

This video is a classic and still suffers from the same problem it did ages ago. That is to say, why did the creator of this video purposely leave out the planet URANUS?

[Bergerac]

Very informative. A third grade level learning device intented for problem students.
The informed thinker would probably be aware that stars occur in binary and trinary and quadruple stellar systems with each star orbiting the other in an orderly manner with each star parenting a distinct lot of terrestrial and gaseous planets.
An issue which must be addressed concerns the mass of supergiant and hypergiant stars. The larger stars are basically spheres of hot gas with a central core of dense matter.
Relative relationship of multi star formations deserves attention: in the more exotic circumstances a sun-like star may be expected to orbit a field of blue tens of light years distant. Another viable probability is a sun-like star orbiting a blue supergiant at apprx 0.11 light years distance. What would be the mass-orbital identity of such a stellar association? Only a sophisticated computer programs capable of modeling existing solar systems can answer that question.
Stellar relationships involving a sun-like star orbited by a red dwarf probably contain a myriad of terrestrial planets similar to the Earth. A neat example would be a sun-like star orbited by a red dwarf at a distance of apprx 300 billion km.
Mass of sun-like star: 0.97 sun; diameter: 1.1 sun
Mass of red dwarf: 0.48 sun; diameter: 0.55 sun
A central sun-like star may also be accompanied by a brown dwarf stellar body; the companion brown dwarf orbiting at a distance of apprx 100 billion km. The solar system is an example of a G type star with a dim brown dwarf companion.

[Bob Stuart]

I'd like to see the stars that are smaller than our sun in one of these arrays.

[jrzedevl]

Planets and Sun are rotating in reverse.

Either that or they're upside down

[SomeSleeplessGuy]

Is my maths wrong, or should it take about 1500 years to fly around the supergiant, not 1100?
d=2.8 bnkm
circumference = pi(d) = 8.8bnkm
vel = 900km/h
therefore flight duration = 9.77 million hours = 1535 years.

Or maybe they're not going around the equator...

[Uwe]

"No, you are NOT the center of the universe!"
In Fact that's hard to be proven, to be completely honest. ^^
A better expression would be "Maybe you ARE the center of the universe, but who gives a F***!"
Thanks for the nice video, a little annoying music (yep, I'm getting old).

[Guest]

It would be nice to also compare the largest stars with the size of the earth orbit (how far would the earth be from the "surface" of the red giants (assuming it is not inside the star!)
Of course this does not imply that such an orbit would be possible (the planet could be crushed by the gravity gradient?)

[Borc]

"No, you are NOT the center of the universe!"
In Fact that's hard to be proven, to be completely honest. ^^
A better expression would be "Maybe you ARE the center of the universe, but who gives a F***!"
Thanks for the nice video, a little annoying music (yep, I'm getting old).

This exactly.

[yannick]

There is an inaccuracy near the end of the movie: I am indeed the center of the universe.

[ro-star]

here is a much better video (our small world, 65sec), hopefully you'll put this one on apod too;

http://www.youtube.com/watch?v=855LIxE0qP0

yes, it has Uranus!

yes, Saturn has rings!

yes, the planets rotate in the correct direction! (well, in the apod video today, they also rotate correctly, if viewed "upside down" with the south pole at the "top", where top/bottom make no sense in space anyway)

yes, it has binary stars!

yes, it compares 17 stars (including sun), whereas today's apod video compares only 10 stars (including sun);

check it out

[ro-star]

also, to answer the question in the video, how could one possibly ever imagine a diameter of 2.8 billion km, that is too easy to imagine;

given Saturn's orbit has a radius of 1.46 billion km, your 2.8 billion km diameter star would fit inside Saturn's orbit, how much easier than that could it get?

[Ann]

I have an interest in the way we visualize the larger stars. I know we've never resolved any star other than our sun into much more than a blurry blip 4 pixels across, so we may never have a direct image of one, but do we know enough about them to guess a little better at their appearance? For instance, would the edge of the star be so clearly defined or would it be kind of tattered like a cloud? Or maybe blurred like a fog settled close to the ground? Or perhaps there is a visible layering effect? I also wonder if we could look at the star a bit longer with our own eyes without some sort of filter.

Jim Kaler wrote about Betelgeuse:
The star is so big that its angular diameter is easily measured. Indeed it was the first to have such a measure, of 0.047 seconds of arc, from which we find a true radius of between 4.1 (compromise distance) and 4.6 (larger distance) AU, considerably greater.

However, the star is surrounded by a huge complex pattern of nested dust and gas shells, the result of aeons of mass loss, that extends nearly 20,000 AU away (Betelgeuse so far having lost over a solar mass). That, an extended atmosphere, and the pulsations make it difficult to locate an actual "surface" to tell just how large the star actually is.

Moreover, because of changes in gaseous transparency, the "size" of the star depends on the color of observation. Long-wave infrared measures give a vastly larger radius of up to 5 AU and greater, as big as the orbit of Jupiter, while shorter-wave infrared light gives as small as 3 AU. Moreover still, infrared measures reveal Betelgeuse to be shrinking (by some 15 percent over about 20 years), and other measures show that the star is not even round, but somewhat oval.

Ann

[Guest]

also, to answer the question in the video, how could one possibly ever imagine a diameter of 2.8 billion km, that is too easy to imagine;
given Saturn's orbit has a radius of 1.46 billion km, your 2.8 billion km diameter star would fit inside Saturn's orbit, how much easier than that could it get?

I was going to suggest showing the limit of the solar system. This is the furthest distance that humans have travelled away from their home.

[owlice]

This video is a classic and still suffers from the same problem it did ages ago. That is to say, why did the creator of this video purposely leave out the planet URANUS?

Click to play embedded YouTube video.

[JohnD]

Hugo,
By definition, a Black Hole has no size. It is a point in space with no diameter at all.
Perhaps a BH should be the focus of a similar size comparison video going smaller rather than larger.
This video ends at the Plank length - a BH should be smaller than that!
https://www.youtube.com/watch?v=MKtfBd8QnYE

John

[tallahassee]

The planets are rotating in the wrong direction! Our Sun, too, I think.

[M913]

This is one of the most phenomenally relevant and hilarious apods ever; and they're all great. I am laughing in delight at our significance while in total awe of being alive to see this stuff, thanks to you.

[gpryde]

I am the center of the Universe, you are the center of the universe, even betelgeuse is the center of the universe. That is, based on our current understanding of cosmology.

[neufer]

Is my maths wrong, or should it take about 1500 years to fly around the supergiant, not 1100?
d=2.8 bnkm
circumference = pi(d) = 8.8bnkm
vel = 900km/h
therefore flight duration = 9.77 million hours = 1535 years.

Your maths wrong(; get some more sleep):
9.77 million hours = 407,000 days = 1115 years.

And since VY Canis Majoris is now thought to be only
1.975 bnkm in diameter that reduces to ~785 days.

<<VY Canis Majoris (VY CMa) is a red hypergiant in the constellation Canis Major. It is one of the largest known stars by radius and also one of the most luminous of its type. It is approximately 1,420 ± 120 solar radii (6.6 astronomical units), about 1,975,000,000 kilometres in diameter, and about 1.2 kiloparsecs (3,900 light-years) distant from Earth. VY CMa is a single star categorized as a semiregular variable and has an estimated period of 2,000 days. It has an average density of 5 to 10 mg/m3. If placed at the center of the Solar System, VY Canis Majoris's surface would extend beyond the orbit of Jupiter, although there is still considerable variation in estimates of the radius, with some making it larger than the orbit of Saturn. The first known recorded observation of VY Canis Majoris is in the star catalogue of Jérôme Lalande, on 7 March 1801, which lists VY CMa as a 7th magnitude star. Further 19th-century studies of its apparent magnitude demonstrate that the star has been fading since 1850.>>

<<NML Cygni or V1489 Cygni is a red hypergiant star and the largest star currently known, at about 1,650 times the Sun's radius or 7.67 a.u. It was discovered in 1965, by Neugebauer, Martz & Leighton. It is one of the extreme luminous supergiant stars. Its distance from Earth is estimated to be around 1.6 kpc, or about 5,300 light-years. This star has a dusty environment surrounding it, and it exhibits a [ lima / fava / string / human ] bean-shaped asymmetric nebula which is coincident with the distribution of its H₂O vapor masers. It is a semiregular variable star with a period of around 940 days. The bolometric luminosity for this star is near 3 × 10⁵ L☉. Its bolometric magnitude is around −9.0. It is one of the most luminous cool hypergiant stars.

From the observations, it is estimated that this star has two discrete optically thick envelopes of dust and molecules. The optical depth of the inner shell is found to be 1.9 while that of the outer one is 0.33. The star has one of the largest mass loss rates at around 2 × 10^-4 M☉ per year. These dust envelopes are formed due to the strong post-mainsequence wind velocity and the high mass emission rate. The post-MS wind velocity is 23 km/s. Because of its unique location within the Milky Way the star does not dominate its local interstellar environment.

NML Cyg is a massive oxygen-rich star. Its composition began to be revealed with the discovery of OH masers (1612 MHz) in 1968 (Wilson and Barrett). The presence of molecules like H₂O, SiO, CO, HCN, CS, SO, SO₂ and H₂S was also revealed in the later years>>